Numerical taxonomy is a system of grouping species using numerical methods based on their character states. It involves assigning numerical values to characteristics, estimating resemblance between organisms, and performing cluster analysis to group similar organisms. The basic components of numerical taxonomy are operational taxonomic units, unit characters, and estimating resemblance between units. Hierarchical clustering is used to group units into a tree-like structure of clusters. While numerical taxonomy provides a standardized, quantitative approach, character selection can impact results if not done adequately.

2. Numerical taxonomy
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3. Taxonomy
• Plant taxonomy is a branch of botany that deal with the
identification, description, classification and giving
names to the plants based on their morphology and
physiology by following certain rules.

4. Numerical taxonomy
• Numerical taxonomy is a system of grouping of species
by numerical methods based on their character states.
• Application of mathematical procedures to numerically
encoded characters.

5. Start and development
• The period from 1957 to 1961 saw the development.
• Michel Adanson, a French botanist, who for the first time
put forward a plan for assigning numerical values.
• Sneath and sokal: published “principles of numerical
taxonomy” in 1963.
• Important names are Michener, Sokal, Sneath, Cain,
Harrison.

6. Principles
• Individuals are selected
• Characters are spotted
• Resemblance is established
• Discrimination is set

7. Bases of classification:

8. Components of numerical
taxonomy
• Operational taxonomic units
• Unit characters
• Estimation of resemblance
• Cluster analysis

9. OTUs
• Operational taxonomic unit is the basic unit in numerical
taxonomy. It can be an individual, species, genus, family,
order or class.

10. Unit characters
• Unit characters are the characters used in numerical
taxonomy.
Types of unit characters:
Binary Multistate Admissible inadmissible
Qualitative Quantitative

11. Selection of characters
Sneath and Sokal (1973) have given the following suggestions for proper
selection of unit characters:
• a.They should come from all parts of the organism.
• b.They should belong to all the stages of the life cycle of the organism.
• c.Variable characters within the group should be used.
• d. Due attention should be given to characters related to morphology,
physiology, ecology and
• distribution of the organisms

12. Estimation of resemblance
• The resemblance between two OTUs is estimated or
measured either:
In terms of similarity i.e., percentage of characters in which
they agree, or
In terms of dissimilarity i.e., percentage of characters in
which they do not agree.

13. Methods of estimation
Coefficients
of association
Coefficients
of correlation
Measure of
taxonomic
distance b/w
OTUs
S=
Ns
Ns+Nd
Evaluation of Some Coefficients for Use in Numerical
Taxonomy of Microorganisms
B. AUSTIN AND R. R. COLWELL

14. Cluster analysis
• class of techniques that are used to classify objects or
cases into relative groups called clusters.
• Monothetic and multithetic clustering.
• Hierarchial and n0n – hierarchial analysis.

15. Cluster analysis
• Monothetic system — This system employs the
attributes one at a time. The monothetic method
obviously leads to artificial clustering.
• Multithetic system _ this system employs many
attributes at a time.

16. Hierarchial clustering
• Hierarchical clustering an algorithm that groups similar
objects into groups called clusters.
• The endpoint is a set of clusters, where each cluster is
distinct from each other cluster
• A hierarchical procedure in cluster analysis is
characterized by the development of a tree like structure.

17. Distance matrix

19. Non hierarchial clustering

20. Dendrogram types

21. Merits:
• The data of conventional taxonomy is improved by numerical taxonomy as it utilizes
better and more number of described characters.The data are collected from a
variety of sources, such as morphology, chemistry, physiology, etc.
• As numerical methods are more sensitive in delimiting taxa, the data obtained can
be efficiently used in the construction of better keys and classification systems,
creation of maps, descriptions, catalogues, etc. with the help of electronic data
processing systems.
• The number of existing biological concepts have been reinterpreted in the light of
numerical taxonomy.
• Numerical taxonomy allows more taxonomic work to be done by less highly skilled
workers.

22. Demerits:
• The numerical methods are useful in phenetic classifications and not phylogenetic
classifications.
• The proponents of “biological” species concept, may not accept the specific limits
bound by these methods.
• Character selection is the greatest disadvantage in this approach. If characters chosen
for comparison are inadequate, the statistical methods may give less satisfactory
solution.
• According to Steam, different taxometric procedures may yield different results.A
major difficulty is to choose a procedure for the purpose and the number of
characters needed in order to obtain satisfactory results by these mechanical aids. It is
necessary to ascertain whether a large number of characters would really give
satisfactory results than those using a smaller number.

23. Conclusion:
Hence numerical taxonomy is the application of mathematical procedures to
numerically encoded characters. The basic components in numeical taxonomy
are OTUs, unit characters and estimation of resemblance. After estimation a
diagram is constructed that is usually called as phenerogram or cladogram on
the basis of similarities and evolutionary trends respectively. The main things in
numerical taxonomy are phonetics and cladistics. Numerical taxonomy is the
modern method of classification. It is beneficial as it makes the data
comprehensive by using computerized and mathematical ways. But like all
other things in the universe it also has some drawbacks.

24. References
• Advanced plant taxonomy by A. K. Mondal (2005)
Chapter no. 09_ numerical taxonomy (Page no. 349_362)
• Plant taxonomy by Stuessy
• https://en.wikipedia.org/wiki/Numerical_taxonomy
• http://www.biologydiscussion.com/plant-taxonomy/numerical-
taxonomy-meaning-merits-and-demerits/30515
• https://www.sciencedirect.com/topics/agricultural-and-biological-
sciences/numerical-taxonomy
• https://www.studyandscore.com/studymaterial-detail/numerical-
taxonomy-and-chemotaxonomy